1. Field of the Invention
The present invention relates to an aqueous dispersion for chemical mechanical polishing. More specifically, the invention relates to an aqueous dispersion that is particularly useful for chemical mechanical polishing of working films of semiconductor devices and the like. The aqueous dispersion for chemical mechanical polishing of the invention has low generation of coarse solids during storage or transport, has less fear of causing scratches and the like, and maintains excellent polishing performance even after storage and transport.
2. Description of the Prior Art
With improved integration and multilayer wiring of semiconductor devices, the technique of chemical mechanical polishing (hereunder referred to as xe2x80x9cCMPxe2x80x9d) is being introduced for polishing of working films and the like. This is a process whereby a wiring material such as tungsten, aluminum, copper or the like is embedded in a hole or groove formed in an insulating film on a processing wafer and then polishing is performed to remove the excess wiring material to thereby form the wiring. For such polishing, the abrasive particles used are usually inorganic particles of alumina, silica, zirconia or the like, or organic particles of polystyrene, polymethyl methacrylate or the like. Aqueous dispersions containing these abrasive particles can accomplish polishing of working films at sufficient rates.
Resinous or metallic sealed containers are commonly used for storage or transport of aqueous dispersions for CMP, but increasing temperature during storage can cause evaporation of moisture at the gas-liquid interface, which upon drying results in production of solids made of the abrasive particles. During transport, vibrations on the container can result in adhesion of the aqueous dispersion to the inner wall surface, with evaporation of moisture from the adhered aqueous dispersion leading to production of dried solids. These solids become included in the aqueous dispersion as coarse particles, and during polishing these coarse particles can cause scratching of polishing surfaces. They can also lead to clogging of conduits used for supply of the aqueous dispersion.
It is an object of the present invention to overcome the problems of the prior art described above, by providing an aqueous dispersion for CMP that has low generation of coarse particles from abrasive particles or the like during storage and transport, and maintains excellent polishing performance . In particular, it is an object to provide an aqueous dispersion for CMP that allows polishing of working films and the like of semiconductor devices at a sufficient rate and produces no scratches, even after storage and transport.
The aqueous dispersion for CMP according to the first aspect of the invention is characterized by comprising abrasive particles, an amphipathic compound and water.
The aqueous dispersion for CMP according to the second aspect of the invention is characterized by comprising abrasive particles and water, wherein a boundary film is formed at the interface between the aqueous dispersion and the air.
The boundary film according to the second aspect of the invention is composed of an amphipathic compound to inhibit escape of moisture, as according to the third aspect of the invention. That is, the aqueous dispersion for CMP according to the third aspect is characterized in that the boundary film of the second aspect of the invention is composed of an amphipathic compound. According to the second and third aspects of the invention, the xe2x80x9cboundary filmxe2x80x9d formed at the interface between the aqueous dispersion and the air inhibits production of solids due to escape of moisture from the gas-liquid interface during storage or from the aqueous dispersion adhering to the upper inner wall surface due to vibrations on the container during transport.
The fourth aspect of the invention specifies the preferred range for the HLB value which represents the hydrophilic/lipophilic balance of the amphipathic compound, and it is characterized in that the HLB value is greater than 0 but no greater than 6.
According to the first to third aspects of the invention, there is provided an aqueous dispersion for CMP that has low generation of coarse solids from abrasive particles and the like, maintains adequate polishing rate even after storage and transport, and produces no scratching. The aqueous dispersion is particularly useful for CMP of working films on semiconductor devices. Furthermore, by using specific amphipathic compounds as according to the fourth aspect, it is possible to produce aqueous dispersions for CMP that maintain even more stable polishing performance.
The xe2x80x9cabrasive particlesxe2x80x9d are not particularly restricted, and either inorganic particles or organic particles, or organic/inorganic composite particles, may be used.
As inorganic particles there may be mentioned silica, alumina, ceria, zirconia, titania and the like. For high purity, the inorganic particles are most preferably synthesized by a fumed process (high-temperature flame hydrolysis), a gas phase process by Nanophase Technology Corp. (metal vapor deposition oxidation) or a sol-gel process whereby synthesis is accomplished by hydrolyzing condensation from a metal alkoxide.
As organic particles there may be used polymer particles composed of a thermoplastic resin made of polystyrene and a styrene-based copolymer, or a (meth)acrylate resin such as polymethyl methacrylate and an acryl-based copolymer. There may also be used polymer particles composed of thermosetting resins such as phenol resin, urea resin, melamine resin, epoxy resin, alkyd resin or unsaturated polyester resin.
Polymer particles composed of a thermoplastic resin and polymer particles composed of a thermosetting resin may also be used in combination.
As organic/inorganic composite particles there may be mentioned composite particles which are organic particles evenly coated with inorganic particles, composite particles wherein a polymer is adhered or bonded to inorganic particles, or composite particles wherein a polymer film is formed on the surface of inorganic particles. Inorganic particles, organic particles and organic/inorganic composite particles may also be used in combination of two or more.
The content of the abrasive particles may be 0.05-20 parts by weight (hereunder referred to as xe2x80x9cpartsxe2x80x9d), especially 0.07-15 parts and more preferably 0.1-10 parts, with respect to 100 parts of the aqueous dispersion, in terms of the total of the inorganic particles, organic particles and organic/inorganic composite particles. If the abrasive particle content is less than 0.05 part it may not be possible to achieve an aqueous dispersion with sufficient polishing performance. A content of greater than 20 parts is also not preferred as the cost is increased and the stability of the aqueous dispersion may be reduced.
The xe2x80x9camphipathic compoundxe2x80x9d is a compound having both a hydrophilic portion and a lipophilic portion in the molecule. The hydrophilic portion may be a hydroxyl group, ester group, carboxyl group or the like, and the lipophilic portion may be a relatively long-chained hydrocarbon group. As such compounds there may be mentioned (1) aliphatic alcohols, (2) fatty acids, (3) sorbitan fatty acid esters, (4) glycerin fatty acid esters, (5) propylene glycol fatty acid esters and (6) esters of polyethyleneglycol and fatty acids. The hydrocarbon groups of these compounds may have unsaturated bonds, and they may be linear or branched.
The following compounds may be mentioned as specific amphipathic compounds of the types listed above.
(1) Aliphatic alcohols: Monoalcohols of 6-18 carbons and polyols such as diols of 12-18 carbons and triols of 12-18 carbons are suitable for use. As specific examples there may be mentioned hexanol (HLB value: approx. 6), heptanol, octanol, decanol, dodecanol, tetradecanol (HLB value: approx. 1), hexadecanol, octadecanol and oleyl alcohol.
Preferred among these are monoalcohols of 12-18 carbons, of which tetradecanol, hexadecanol, octadecanol and oleyl alcohol are particularly preferred.
(2) Fatty acids: Fatty acids of 6-18 carbons are suitable for use. As specific examples there may be mentioned caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid and linoleic acid.
Preferred among these are fatty acids of 12-18 carbons, of which stearic acid, oleic acid (HLB value: approx. 1), linolic acid and linoleic acid are particularly preferred.
(3) Sorbitan fatty acid esters: Esters of sorbitan and fatty acids of 12-18 carbons are suitable for use. As specific examples there may be mentioned sorbitan monostearate (HLB value: 4.7), sorbitan distearate (HLB value: 3.5), sorbitan tristearate (HLB value: 2.1), sorbitan tetrastearate (HLB value: 0.5), sorbitan monooleate (HLB value: 4.3), sorbitan dioleate, sorbitan trioleate (HLB value: 1.8) and sorbitan sesquioleate.
Sorbitan is used industrially in the form of mixtures of 1,4-sorbitan, 1,5-sorbitan and 1,4-sorbitan with further dehydration of one molecule. Sorbitan fatty acid esters are mono-, di-, tri- and tetraesters comprising these mixtures with higher fatty acids. Triesters such as sorbitan tristearate and sorbitan trioleate, and sorbitan tetrastearate, are particularly preferred, and usually mixtures of these various esters are used.
(4) Glycerin fatty acid esters: Esters of glycerin and fatty acids of 12-18 carbons are suitable for use. As specific examples there may be mentioned glycerol monostearate (HLB value: 3.8) and glycerol monooleate (HLB value: 2.8-3.5).
(5) Propylene glycol fatty acid esters: Esters of propylene glycol and fatty acids of 12-18 carbons are suitable for use. As specific examples there may be mentioned propylene glycol monostearate (HLB value: 3.4) and propylene glycol monolaurate (HLB value: 4.5).
Among these, propylene glycol monostearate is particularly preferred.
(6) Esters of polyethylene glycol and fatty acids: Monoesters and diesters of 12-18 carbons, and especially 15-18 carbons, with an average molecular weight of 50-500 and especially 100-300, are suitable for use. As specific examples there may be mentioned polyethylene glycol distearate (HLB value: 5.4) and polyethylene glycol dilaurate (HLB value: 2.7).
The esters of (3) to (6) above are formed by low carbon number alcohols and high carbon number acids, but there may also be used esters formed by high carbon number alcohols and low carbon number acids.
These amphipathic compounds may be used alone, or two or more of the compounds of (1) to (6), or two or more different types from among those of (1) to (6), may also be used in combination.
The content of the amphipathic compound may be 0.00001-10 parts, preferably 0.00005-5 parts, especially 0.0001-1 part and more preferably 0.0005-0.1 part, with respect to 100 parts of the aqueous dispersion.
The amphipathic compound may be directly added while stirring the aqueous dispersion, or it may be added after pre-dilution with water. In the case of an aliphatic alcohol or fatty acid, it may be emulsifying with a prescribed amount of water or with water and an emulsifying agent prior to its addition to the aqueous dispersion. For example, 60-80 parts of water and preferably 0.01-0.1 part of an anionic or nonionic surfactant may be combined with 20-40 parts of the amphipathic compound and stirred for emulsification, prior to its addition.
The HLB value is preferably greater than 0 but no greater than 6, especially 0.1-6, more preferably 0.3-5, and most preferably 0.5-4. The HLB value is preferably not greater than 6, because this may prevent formation of a boundary film capable of adequately inhibiting escape of moisture, thus resulting in production of solids upon drying.
The HLB value is the value determined based on the molecular structure or experimentally, and numerous equations have been proposed for determining the HLB value. For example, the following equation proposed by Griffin may be used for the calculation.
HLB value=(wt % of hydrophilic groups)/5
The aqueous dispersion for CMP according to the invention may be prepared by mixing the abrasive particles and amphipathic compound in water (ion-exchanged water or the like). The medium for the aqueous dispersion may be water or a mixed medium composed mostly of water, such as a mixture of water and methanol, but water alone is particularly preferred.
The aqueous dispersion may also contain an oxidizing agent. The oxidizing agent need only be water-soluble, and there are no particular restrictions on the type thereof. Specifically there may be mentioned hydrogen peroxide, organic peroxides such as peracetic acid, perbenzoic acid and tert-butylhydroperoxide, nitric acid compounds such as nitric acid and iron nitrate, perhalogenated compounds such as perchloric acid, transition metal salts such as potassium ferricyanide, persulfuric acid salts such as ammonium persulfate, and hetero polyacids. Including such oxidizing agents can provide improved polishing rate for polishing of working films and the like.
The content of the oxidizing agent may be 0.05-15 parts, especially 0.1-10 parts and more preferably 0.2-8 parts, with respect to 100 parts of the aqueous dispersion. If the content is less than 0.05 part the polishing rate of the aqueous dispersion will not be sufficiently increased. A content of 15 parts can adequately improve the polishing rate, and a greater amount exceeding 15 parts is not preferred since it can produce corrosion on the polishing surface and thus poses a risk for handling.
By adding an acid for pH adjustment, it is possible to further improve the dispersability, stability and polishing rate of the aqueous dispersion. The acid is not particularly restricted, and any organic acid or inorganic acid may be used. As organic acids there may be mentioned gluconic acid, lactic acid, citric acid, tartaric acid, malic acid, glycolic acid, malonic acid, formic acid, oxalic acid, succinic acid, fumaric acid, maleic acid and phthalic acid. These organic acids may be used alone or in combinations of two or more. As inorganic acids there may be mentioned nitric acid, hydrochloric acid and sulfuric acid, and these inorganic acids may also be used alone or in combinations of two or more. Combinations of organic acids and inorganic acids may also be used. These acids may be used at up to 10 parts, and especially from 0.001-8 parts to 100 parts of the aqueous dispersion. The acid content is preferably in the range of no greater than 10 parts as this will provide an aqueous dispersion with excellent dispersability and sufficient stability.
By adding a base for adjustment of the pH, it is possible to further improve the dispersability, corrosion resistance, stability and polishing rate of the aqueous dispersion. The base is not particularly restricted, and any organic base or inorganic base may be used. As organic bases there may be mentioned ethylenediamine, ethanolamine and 4-vinylpyridine. As inorganic bases there may be mentioned ammonia, potassium hydroxide, sodium hydroxide and lithium hydroxide. These bases may be used alone or in combinations of two or more. The bases may be used at up to 10 parts, and especially from 0.001-8 parts to 100 parts of the aqueous dispersion. The base content is preferably in the range of no greater than 10 parts as this will provide an aqueous dispersion with excellent dispersability and sufficient stability.
Aqueous dispersions according to the first to third aspects of the invention are particularly useful for CMP of working films on semiconductor devices. As working films there may be mentioned silicon oxide films, amorphous silicon films, polycrystalline silicon films, single-crystal silicon films, silicon nitride films, pure tungsten films, pure aluminum films or pure copper films, as well as alloy films of tungsten, aluminum and/or copper with another metals, that are formed on semiconductor substrates in manufacturing processes for semiconductor devices such as VLSIs and the like. Barrier metal layers composed of metals such as tantalum and titanium or oxides or nitrides thereof, may also be mentioned as working films.
The CMP of a working film or the like on a semiconductor device with an aqueous dispersion may be accomplished using a commercially available CMP apparatus (such as Model xe2x80x9cLGP510xe2x80x9d or xe2x80x9cLGP552xe2x80x9d by Lapmaster SFT Corp., a Model xe2x80x9cEPO-112xe2x80x9d or xe2x80x9cEPO-222xe2x80x9d by Ebara Laboratories Co., Ltd., or a Model xe2x80x9cMirraxe2x80x9d by Applied Materials Corp.). After the polishing, it is preferred to remove the residual abrasive particles from the polishing surface. The particle removal can be accomplished by a common washing method, and in the case where the abrasive particles are organic particles, the polishing surface can be heated at high temperature in the presence of oxygen to burn the particles for their removal. As the method for burning there may be mentioned exposure to oxygen plasma, or ashing treatment with plasma whereby oxygen radicals are supplied in a downflow; these allow the residual organic particles to be easily removed from the polishing surface.
The present invention will now be explained in greater detail by way of examples.
(1) Production of Aqueous Dispersion Containing Abrasive Particles